1. Field of the Invention
This invention relates to a rebound stop for a shock absorber and, more particularly, to a hydraulic assisted rebound stop assembly.
2. Description of the Related Art
Typically, shock absorbers are designed such that the damping rate of the shock absorber becomes higher at the extreme ends of the rebound and compression strokes. The additional damping provided at these extreme ends prevents an abrupt halt to the piston rod travel as well as jarring metal-to-metal contact between the various parts in the shock absorber. A variety of mechanisms have been proposed to provide a higher damping rate at the two extremes. For example, U.S. Pat. Nos. 4,527,674 and 4,397,452, both assigned to the assignee of the present invention, disclose a rebound stop assembly including an elastomeric ring interposed between two collars, forming an annular chamber therebetween. At the end of the rebound stroke of the piston rod, the rebound stop assembly is compressed between the shoulders of the piston rod and the rod guide of the shock absorber until the elastomeric ring deforms to abut the inner wall of the working cylinder of the shock absorber. As the elastomeric ring deforms, the annular chamber decreases in volume. A restrictive passage formed between the elastomeric ring and the working cylinder of the shock absorber restricts the fluid flow from the annular chamber. The compression of the elastomeric ring and the restricted fluid flow provides additional damping at the end of the rebound stroke. It has been found, however, that after prolonged use under extreme temperatures not typically encountered in normal driving conditions, the elastomeric ring may degrade and the effectiveness of the rebound stop assembly maybe reduced or completely eliminated.
Secondary pistons also have been proposed to provide additional damping at the extreme end of the shock absorber. For example, U.S. Pat. No. 4,852,703 discloses the use of an additional piston fixed to the piston rod within the working cylinder of the shock absorber to provide additional damping at the end of the rebound stroke. As the piston rod nears the end of the rebound stroke in the '703 patent, the additional piston is forced into a fixed, tubular cylinder secured to the closed end of the shock absorber. Additional damping is provided by forcing hydraulic fluid from this tubular cylinder around the periphery of the additional piston. A similar type of rebound stop assembly is shown in GB 2,158,181, wherein a spring loaded additional piston is disposed above the main piston of the shock absorber. An elongated tubular cylinder extending the entire length of the working cylinder of the shock absorber is provided in a location opposite the outer surface of the additional piston. The additional piston travels within this fixed cylinder and additional damping is provided by forcing fluid from above the piston to below the piston. These types of rebound stop assemblies require elongated cylindrical tubings contained within the working cylinder of the shock absorber and are difficult and expensive to manufacture. The tolerances required to create effective damping are difficult to ensure.
Therefore, it is an object of the present invention to provide a hydraulic mechanical rebound stop assembly which effectively dampens motion of the piston at the end of its stroke while being economical to manufacture and assemble.